1. Field of the Invention
This invention relates to characterization of particles entrained in a fluid carrier medium. It is particularly directed to a combination of optically-based characterization of particles and electrically-based detection of a fluid boundary and/or one or more particles.
2. State of the Art
Optically-based data acquisition has been in existence for a very long time. Exemplary such optically-based data acquisition includes a human examining stained slides under a microscope, and counting particles (e.g. cells) contained on the slide. Such work is tedious, and errors are difficult to avoid. Computerized digital image evaluation has been developed to avoid some of the difficulties associated with manual optical data collection.
Electrically-based data acquisition of particles entrained in a fluid carrier has also been in existence for a very long time. Pioneering work in particle detection by measuring impedance deviation caused by particles flowing through a small aperture between two containers of electrically conductive fluid is disclosed in U.S. Pat. No. 2,656,508 to W. H, Coulter. Coulter's name is now associated with the principle of particles causing a change in electric impedance as they occlude a portion of the aperture. Since publication of his patent, considerable effort has been devoted to developing and refining sensing devices operating under the Coulter principle. Relevant US patents include U.S. Pat. No. 5,376,878 to Fisher, U.S. Pat. No. 6,703,819 to Gascoyne et al., U.S. Pat. No. 6,437,551 to Krulevitch et al., U.S. Pat. No. 6,426,615 to Mehta, U.S. Pat. No. 6,169,394 to Frazier et al., U.S. Pat. No. 6,454,945 and U.S. Pat. No. 6,488,896 to Weigl et al., U.S. Pat. No. 6,656,431 to Holl et al., and U.S. Pat. No. 6,794,877 to Blomberg et al. Patent application 2002/117,517 to Unger et al. is also relevant. Each above-referenced document is hereby incorporated by reference, as though set forth herein in their entireties, for their disclosures of relevant technology and structure employed in various sensor arrangements.